Young adults between the ages of 18 and 29 report the highest rate of past month marijuana (MJ) use. Young adults also have high rates of sleep disturbance that can affect wake-time functioning: school, work, cognitive and social functioning, mood, and driving risk. Evidence suggesting that MJ is associated with sleep disturbance makes the relationship between MJ and sleep a subject of major public health significance. The effects of MJ use and sleep disturbance on daytime functioning across a range of MJ use frequency has not been studied, nor has the relationship of subjective sleep reports to objective measures of sleep in community- based young adults. Nearly all controlled studies of MJ and sleep have occurred in the context of studying MJ withdrawal where laboratory polysomnography has been used to describe sleep disturbance during discontinuation of heavy MJ use. Yet most young adult MJ users are not heavy users, and few seek formal substance abuse treatment with a goal of abstinence. Thus, although MJ use impacts sleep, the relationship between MJ and sleep remains unstudied at the MJ use levels most common in the community. Eighty MJ users and twenty MJ nonusers, without and without sleep disturbance, will receive a baseline assessment followed by 21-days of actigraphy and sleep diaries that include measures of daytime function collected via daily phone contact, with a final interview assessment on day 22. The Specific Aims of this study are: 1) To investigate sleep disturbance among young adults aged 18-29 who use marijuana and compare with a control group of MJ nonusers 2) To investigate the interrelationships between sleep disturbance and daytime functioning among MJ users and compare with MJ nonusers Quantifying the relationship between MJ and sleep disturbance in young adults can provide data that can help formulate intervention strategies, such as public health campaigns to increase awareness of this clinically meaningful consequence of MJ use. It would also provide impetus for primary care and mental health providers to discuss the MJ-sleep connection at the point of contact with MJ users.